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Author Topic: Exporting files to a specific file size  (Read 1861 times)

marcgoldring

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Exporting files to a specific file size
« on: April 22, 2017, 08:32:24 AM »

I want to export files at 300 DPI as TIFFs no larger than 25MB. I don't see a way to select file size in the image sizing section of the export dialogue. Is it best to just use trial and error with megapixel size? Or is there a more efficient way to do this?

Thanks in advance.

Marc
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #1 on: April 22, 2017, 09:32:21 AM »

Try this:

P.S. The "resolutions per inch" is my screen resolution. Adjust to taste.

P.P.S. I also assume you meant PPI not DPI

marcgoldring

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Re: Exporting files to a specific file size
« Reply #2 on: April 22, 2017, 10:32:29 AM »

Thanks for this, Slobodan!

But I don't understand how you decided to use 5 MP rather than some other value...

M


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Marc Goldring
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #3 on: April 22, 2017, 10:35:54 AM »

...But I don't understand how you decided to use 5 MP rather than some other value...

I didn't. It was pre-filled. I just used it as an example. Is this better:

marcgoldring

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Re: Exporting files to a specific file size
« Reply #4 on: April 22, 2017, 11:01:29 AM »

Yes, and that's what I did but I got files that ranged in size from about 15MB  to almost 90.

Argh!!

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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #5 on: April 22, 2017, 11:52:52 AM »

Yeah, it doesn't work.

I guess it requires a lot of computation that the program is not designed to handle. With JPEG, it has a compression algorithm to play with (and even then it is not very precise). For TIFF, the only thing the program could alter are image dimensions. And to get there, it requires a square root calculation.

To get to, say for the simplicity sake, 24 MP, if an RGB file (i.e., color), it means 8 MP per color (if 8 bits). If a standard full-frame ratio of 1.5, it means the following calculation:

8 divided by 1.5 = 5.333
Square root of 5.33 = 2.309

In other words, you need a file that is 2309 px short and 3464 px long to get to exactly 24 MP.

If you work with a 16 bit file, that would result in a 48 MP (or your calculation would be altered to start with 4 divided by 1.5...)



« Last Edit: April 23, 2017, 08:31:26 AM by Slobodan Blagojevic »
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marcgoldring

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Re: Exporting files to a specific file size
« Reply #6 on: April 23, 2017, 06:51:08 AM »

Ok, well, sure... I can follow that.

So it seems like my original impulse - trial and error - is the way to go here.

Thanks for the explanation!

All best,

Marc
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Rhossydd

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Re: Exporting files to a specific file size
« Reply #7 on: April 23, 2017, 08:12:24 AM »

To get to, say for the simplicity sake, 24 MP,
The OP is asking about MB, not MP. A big difference there.

The output file size will vary with the type of TIFF being output. It can either be uncompressed or use ZIP compression. If the later, file size will vary with image content as some images will compress further than others, eg if there are large amounts of continuous tone in them.
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #8 on: April 23, 2017, 08:29:18 AM »

The OP is asking about MB, not MP. A big difference there...

Like?

Rhossydd

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Re: Exporting files to a specific file size
« Reply #9 on: April 23, 2017, 08:58:43 AM »

Like?
Do you not realise the difference between MP (Megapixels) the number of pixels in an image, ie a fixed number and MB (megabytes) the amount of file space a files takes up which is dependant of file type together with the type and amount of data compression that's applied to that file  ?

This is page one digital imaging.
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #10 on: April 23, 2017, 09:40:53 AM »

...data compression...

The assumption of the OP was that we are talking about uncompressed files. My numerical example was clearly about uncompressed files.

Rhossydd

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Re: Exporting files to a specific file size
« Reply #11 on: April 23, 2017, 09:50:33 AM »

The assumption of the OP was that we are talking about uncompressed files.
No. There's no mention of compression at all in the OP's posts. It's almost certainly where the misundertsandings are coming from.
Talk of Megapixels is just a total distraction.
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #12 on: April 23, 2017, 10:27:36 AM »

No. There's no mention of compression at all in the OP's posts...

Precisely the reason for assuming un-compressed files.

Quote
... It's almost certainly where the misunderstandings are coming from.

What misunderstandings? I clearly indicated, in the screenshot that I attached to my reply that it was un-compressed. The OP, in his subsequent post, did not indicate he wanted compressed files either.

Quote
... Talk of Megapixels is just a total distraction.

Pardon me for using Adobe's own notation.

Rhossydd

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Re: Exporting files to a specific file size
« Reply #13 on: April 23, 2017, 10:34:37 AM »

Precisely the reason for assuming un-compressed files.
That is no reason for any assumption.
If you want to draw any conclusion from that, no mention of compression either way most likely suggests a lack of awareness of the issue.

There's still no reason at all to start going into megapixel issues, it's an irrelevant distraction.
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #14 on: April 23, 2017, 10:36:48 AM »

... There's still no reason at all to start going into megapixel issues, it's an irrelevant distraction.

Exactly! But who is going there, except you?

Rhossydd

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Re: Exporting files to a specific file size
« Reply #15 on: April 23, 2017, 10:45:45 AM »

Exactly! But who is going there, except you?
You're the one that brought the issue up in the first place discussing image dimensions rather than file size.
When discussing MB, as in the first post, it's an irrelevance.
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #16 on: April 23, 2017, 11:46:47 AM »

You're the one that brought the issue up in the first place discussing image dimensions rather than file size.
When discussing MB, as in the first post, it's an irrelevance.

Maybe because changing image dimensions is the ONLY way to get a TIFF file to a desired MB (MP) size with uncompressed files?

With compressed files, one can certainly use trial and error, but that is a looooong road, and you may not even get where you wanted in the end.

Let's look at an example (see screenshots): compressing the file gives only 15% less. Specifying 25 MB/MP results in a larger (!) file, as Lightroom inexplicably increases the original file dimensions (!). The ONLY way to arrive to a desired output size is to manually specify file dimensions.

Note: all the examples are with 16bit files (hence 48 MB/MP instead of 24 - which is the number I used in the previous calculation).

 

Rhossydd

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Re: Exporting files to a specific file size
« Reply #17 on: April 23, 2017, 11:50:03 AM »

Maybe because changing image dimensions is the ONLY way to get a TIFF file to a desired MB (MP) size with uncompressed files?
That's not the question though. There's been NO MENTION of needing uncompressed files.
You're not being at all helpful here.
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Slobodan Blagojevic

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Re: Exporting files to a specific file size
« Reply #18 on: April 23, 2017, 11:55:16 AM »

That's not the question though. There's been NO MENTION of needing uncompressed files.
You're not being at all helpful here.

Ok, show me how you'd get from an original TIFF file of 120 MB to 48 MB using Lightroom ZIP compression.

Rhossydd

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Re: Exporting files to a specific file size
« Reply #19 on: April 23, 2017, 12:03:45 PM »

Ok, show me how you'd get from an original TIFF file of 120 MB to 48 MB using Lightroom ZIP compression.
Again, it's not relevant to the OP.
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